Non-authenticated users accessing the system are assigned the name anonymous. Assign permissions to the anonymous user to set privileges for anonymous/guest users. The parts of Trac that a user does not have privilege for will not be displayed in the navigation.
In addition to these privileges, users can be granted additional individual rights in effect when authenticated and logged into the system. All logged in users belong to the virtual group authenticated, which inherits permissions from anonymous.

Graphical Admin Tab

To access this tab, a user must have one of the following permissions: TRAC_ADMIN, PERMISSION_ADMIN, PERMISSION_GRANT, PERMISSION_REVOKE. The permissions can be granted using the trac-admin command (more on trac-admin below):

$ trac-admin /path/to/projenv permission add bob TRAC_ADMIN

Then, the user bob will be able to see the Admin tab, and can access the permissions menu. This menu will allow you to perform all the following actions, but from the browser rather than requiring root access to the server. Use at least one lowercase character in user names, as all-uppercase names are reserved for permissions.

From the graphical admin tab, users with PERMISSION_GRANT will only be allowed to grant permissions that they possess, and users with PERMISSION_REVOKE will only be allowed to revoke permissions that they possess. For example, a user cannot grant MILESTONE_ADMIN unless they have PERMISSION_GRANT and MILESTONE_ADMIN, and they cannot revoke MILESTONE_ADMIN unless they have PERMISSION_REVOKE and MILESTONE_ADMIN. PERMISSION_ADMIN just grants the user both PERMISSION_GRANT and PERMISSION_REVOKE, and users with TRAC_ADMIN can grant or revoke any permission.

Available Privileges

To enable all privileges for a user, use the TRAC_ADMIN permission. Having TRAC_ADMIN is like being root on a *NIX system: it will allow you to perform any operation.

Otherwise, individual privileges can be assigned to users for the various different functional areas of Trac (note that the privilege names are case-sensitive):

Ticket System

Modify ticket properties (priority, assignment, keywords, etc.) with the following exceptions: edit description field, add/remove other users from cc field when logged in

TICKET_MODIFY

Includes both TICKET_APPEND and TICKET_CHGPROP, and in addition allows resolving tickets in the default workflow. Tickets can be assigned to users through a drop-down list when the list of possible owners has been restricted.

TICKET_EDIT_CC

Full modify cc field

TICKET_EDIT_DESCRIPTION

Modify description field

TICKET_EDIT_COMMENT

Modify another user's comments. Any user can modify their own comments by default.

All TICKET_* permissions, deletion of ticket attachments and modification of the reporter field, which grants ability to create a ticket on behalf of another user (it will appear that another user created the ticket). It also allows managing ticket properties through the web administration module.

Roadmap

MILESTONE_VIEW

View milestones and assign tickets to milestones.

MILESTONE_CREATE

Create new milestones

MILESTONE_MODIFY

Modify milestones

MILESTONE_DELETE

Delete milestones

MILESTONE_ADMIN

All MILESTONE_* permissions

ROADMAP_VIEW

View the roadmap page, which is not yet the same as MILESTONE_VIEW, see ​#4292

Permission Groups

There are two built-in groups, authenticated and anonymous.
Any user who has not logged in is automatically in the anonymous group.
Any user who has logged in is also in the authenticated group.
The authenticated group inherits permissions from the anonymous group.
For example, if the anonymous group has permission WIKI_MODIFY,
it is not necessary to add the WIKI_MODIFY permission to the authenticated group as well.

Custom groups may be defined that inherit permissions from the two built-in groups.

Permissions can be grouped together to form roles such as developer, admin, etc.

Group membership can be checked by doing a permission list with no further arguments; the resulting output will include group memberships. Use at least one lowercase character in group names, as all-uppercase names are reserved for permissions.

Adding a New Group and Permissions

Permission groups can be created by assigning a user to a group you wish to create, then assign permissions to that group.

The following will add bob to the new group called beta_testers and then will assign WIKI_ADMIN permissions to that group. (Thus, bob will inherit the WIKI_ADMIN permission)

Removing Permissions

Just like permission add, this command accepts multiple privilege names.

You can also remove all privileges for a specific user:

$ trac-admin /path/to/projenv permission remove bob '*'

Or one privilege for all users:

$ trac-admin /path/to/projenv permission remove '*' REPORT_ADMIN

Creating New Privileges

To create custom permissions, for example to be used in a custom workflow, enable the optional ​tracopt.perm.config_perm_provider.ExtraPermissionsProvider component in the "Plugins" admin panel, and add the desired permissions to the [extra-permissions] section in your trac.ini. For more information, please refer to the documentation on the TracIni page after enabling the component.

Default Permissions

By default on a new Trac installation, the anonymous user will have view access to everything in Trac, but will not be able to create or modify anything.
On the other hand, the authenticated users will have the permissions to create and modify tickets and wiki pages.